Satellite positioning reference system and method

ABSTRACT

Methods and apparatuses which use satellite position system (SPS) reference receivers. In one example of the invention, a plurality of SPS reference receivers, such as Global Positioning System (GPS) reference receivers, each having a known position, are dispersed over a geographical region. Each of the SPS reference receivers transmits into a communication network, a representation of at least a portion of a satellite navigation message, such as satellite ephemeris data, received from SPS satellites in view of the particular SPS reference receiver. A plurality of digital processing systems, such as a first and a second digital processing systems, are coupled to the communication network to receive the satellite ephemeris data which is transmitted through the communication network. The first digital processing system receives a first pseudorange data from a first SPS mobile receiver and calculates a first position information of the first SPS mobile receiver from a representation of the first pseudorange data and from satellite ephemeris data received from the communication network. The first digital processing system may also receive pseudorange corrections from the communication network and use these corrections to correct the first pseudorange data to provide the representation of the first pseudorange data. The second digital processing system receives a second pseudorange data from a second SPS mobile receiver and calculates a second position of the second SPS mobile receiver using the second pseudorange data (which may be corrected using pseudorange corrections from the communication network) and using satellite ephemeris data received from the communication network. In one embodiment of this example of the invention, the mobile SPS receivers are communicatively coupled with the digital processing systems in part through a wireless cell based communication system. A further digital processing system may also be coupled to the communication network to receive pseudorange correction data and to provide merged pseudorange correction data to the digital processing systems through the communication network.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 08/842,559, filed on Apr. 15, 1997 by Norman F. Krasner.

BACKGROUND OF THE INVENTION

The present invention relates to satellite position systems which usereference receivers and more particularly to a network of referencereceivers for a satellite positioning system.

Conventional satellite positioning systems (SPS) such as the U.S. GlobalPositioning System (GPS) use signals from satellites to determine theirposition. Conventional GPS receivers normally determine their positionby computing relative times of arrival of signals transmittedsimultaneously from a multiplicity of GPS satellites which orbit theearth. Each satellite transmits, as part of its navigation message, bothsatellite positioning data as well as data on clock timing whichspecifies its position and clock state at certain times; this data,found in subframes 1-3 of the GPS navigation message, is often referredto as satellite clock and ephemeris data and will be referred to assatellite ephemeris data. Conventional GPS receivers typically searchfor and acquire GPS signals, read the navigation message from eachsignal to obtain satellite ephemeris data for its respective satellite,determine pseudoranges to these satellites, and compute the location ofthe GPS receiver from the pseudoranges and satellite ephemeris data fromthe satellites.

Improved position accuracy can be obtained by using a well known andconventional technique referred to as differential GPS. Withconventional differential GPS, a single differential reference stationbroadcasts differential GPS corrections to users in a local region.Thus, there are typically three major components of a conventionaldifferential GPS system. The first component is a reference station at aknown location with a GPS receiver at a known location which is usuallycapable of observing all satellites in view and optionally with softwareat the reference station, which could be imbedded in the GPS receiver,to compute the pseudorange corrections and to code them for specificbroadcast format. Another component is a radio link to transmit thedifferential corrections in real time to mobile GPS receivers. The thirdcomponent is the mobile GPS receiver which also includes a receiver forreceiving the differential corrections broadcast from the referencestation.

The differential GPS corrections are used by the mobile GPS receivers ina conventional manner to correct the pseudorange data which is obtainedby computing the relative times of arrival of signals of GPS signalstransmitted from the GPS satellites. Conventional differential GPS doesnot have to operate in real time or provide corrections to the mobileGPS receiver, although this is often the case. There are manyimprovements on differential GPS which are described in both patent andnon patent literature. These various improvements concentrate on thedifferential correction computation and application algorithms as wellas methods of delivering the differential corrections. The differentialcorrections are for the most part in the measurement domain(pseudorange, accumulated delta-range, and range-rate error estimates).

Conventional differential GPS offers significant position accuracyimprovement if both the reference receiver and the participating mobileGPS receiver are in close proximity to each other. However, the accuracyimprovement from differential GPS degrades as the separation distancebetween the two receivers increases. One solution to rectify thisdegrading of accuracy is to provide a network of GPS reference receiverswhich are dispersed over a geographical area to provide area coveragewhich coincides with the area in which the mobile GPS receivers mayoperate such that they tend to see the same set of satellites. In thisinstance, a mobile GPS receiver may pick up differential correctionsfrom more than one differential reference station, and the mobile GPSreceiver may select those differential corrections for satellites inview based upon the relative proximity between the mobile GPS receiverand the two or more reference stations. The use of multiple referencestations in a differential GPS system is sometimes referred to aswide-area differential GPS (WADGPS).

A further form of a WADGPS reference system includes a network of GPSreference receivers and a master station which is in communication withthe reference stations to receive their measurements and compute amerged set of ephemeris and clock correction estimates for each GPSsatellite observed by the reference stations. This master station canthen provide through a transmitter a differential GPS message withcorrections applicable over an extended range. Examples of suchwide-area differential GPS reference systems include those described inU.S. Pat. Nos. 5,323,322 and 5,621,646.

Independent of the coverage of the particular differential referencesystem, the prime objective of a differential GPS system is to providedifferential service which helps the mobile GPS receiver to removeerrors from the GPS measurements or measurement derived solution. TheGPS system errors that the network attempts to remove is a function ofthe number of reference stations, their spatial placement, and thesophistication of the algorithms implemented at the central processingfacility. The secondary function of the differential networks is toprovide integrity and reliability to the differential service byperforming various checks in the measurement and the state spacedomains.

While the foregoing systems provide improved accuracy to mobile GPSreceivers, those systems are not compatible with a client/server GPSarchitecture in which a mobile GPS receiver functions as a client systemand provides pseudorange measurements to a remotely positioned locationserver which completes the calculations for the position solution byusing the pseudoranges obtained from the mobile GPS receiver and byusing ephemeris data. The present invention provides an improved methodand apparatus allowing flexibility in the positioning of locationservers and also provides for improved efficiency and cost in aclient/server system.

SUMMARY OF THE INVENTION

The present invention provides methods and apparatuses for a satellitepositioning system reference system.

In one aspect of the present invention, an exemplary method processessatellite position information by using at least two SPS referencereceivers. According to this method, a first digital processing systemreceives a first satellite ephemeris data from a first SPS referencereceiver which has a first known position. The first digital processingsystem also receives a second satellite ephemeris data from a second SPSreference receiver having a second known position. The first digitalprocessing system further receives a plurality of pseudorange data froma mobile SPS receiver. The first digital processing system thentypically calculates the position information (e.g. latitude andlongitude and altitude) of the mobile SPS receiver using the pluralityof pseudorange data and at least one of the first satellite ephemerisdata and the second satellite ephemeris data. In one particularembodiment of the present invention, the first satellite ephemeris dataand the second satellite ephemeris data are a subset of the “raw” 50 bpssatellite navigation message received respectively from the first SPSreference receiver and the second SPS reference receiver from thesatellites in view of those two reference receivers. In one example,this satellite navigation message may be the 50 bit per second datamessage encoded into the GPS signals which has been received and decodedby the reference receivers and transmitted to the first digitalprocessing system in real time or near real time.

According to another aspect of the present invention, a system forprocessing satellite position information includes a plurality ofsatellite positioning system (SPS) reference receivers, each having aknown location. It also includes a plurality of digital processingsystems. The plurality of SPS reference receivers is dispersed over ageographical region and each receives satellite ephemeris data fromsatellites in view of the respective SPS reference receiver. Each of theplurality of SPS receivers transmits, into a communication network, thesatellite ephemeris data which it receives. This system also includes aplurality of digital processing systems, each of which is coupled to thecommunication network to receive at least some of the satelliteephemeris data transmitted through the communication network. In oneembodiment, at least two such digital processing systems exist. A firstdigital processing system receives a first plurality of pseudorange froma first mobile SPS receiver and calculates a first position information(e.g. a latitude and a longitude) of the first mobile SPS receiver fromthe first plurality of pseudorange data and from satellite ephemerisdata received from the communication network. Typically, the firstdigital processing system selectively receives from the network theproper satellite ephemeris data for at least those satellites which arein view of the first mobile SPS receiver. A second digital processingsystem receives a second plurality of pseudorange data from a secondmobile SPS receiver and calculates a second position information of thesecond mobile SPS receiver from the second plurality of pseudorange dataand from satellite ephemeris data received from the communicationnetwork. In one example of the invention, the second digital processingsystem selectively receives from the network the appropriate satelliteephemeris for those satellites in view of the second mobile SPSreceiver. In another example of the invention, the first and seconddigital processing systems each receive from the network the mostup-to-date satellite ephemeris data which are in view of the network.

In one further embodiment of the present invention, a further digitalprocessing system may be coupled to the communication network in orderto receive measurements (e.g. differential corrections) from thereference receivers and to produce a set of network differentialcorrections. Various other aspects and embodiments of the presentinvention are further described below.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and notlimitation in the figures of the accompanying drawings in which likereferences indicate similar elements.

FIG. 1 illustrates a cell based communication system having a pluralityof cells each of which is serviced by a cell site, and each of which iscoupled to a cell based switching center, which is sometimes referred toas a mobile switching center.

FIG. 2 illustrates an implementation of a location server systemaccording to one embodiment of the invention.

FIG. 3A illustrates an example of a combined SPS receiver andcommunication system according to one embodiment of the presentinvention.

FIG. 3B illustrates an example of a GPS reference station according toone embodiment of the present invention.

FIG. 4 illustrates an SPS reference receiver network according to oneembodiment of the present invention.

FIGS. 5A and 5B show a flowchart which describes a method according toone embodiment of the present invention.

FIG. 6 shows a data flow for a network correction processor which may beused in one embodiment of the reference receiver network according tothe present invention.

FIG. 7 shows an example of the data flow associated with the locationserver according to one embodiment of the present invention.

DETAILED DESCRIPTION

The present invention provides a network of SPS reference receiverswhich provide at least a portion of the satellite navigation message,such as satellite ephemeris data for use by digital processing systemsin the manner described below. Before describing various details withrespect to this reference system, it will be useful to describe thecontext in which this reference receiver is typically used. Accordingly,a preliminary discussion which refers to FIGS. 1, 2, and 3A will beprovided before discussing the network of SPS reference receivers in thesystem of the present invention.

FIG. 1 shows an example of a cell based communication system 10 whichincludes a plurality of cell sites, each of which is designed to servicea particular geographical region or location. Examples of such cellularbased or cell based communication systems are well known in the art,such as the cell based telephone systems. The cell based communicationsystem 10 includes two cells 12 and 14, both of which are defined to bewithin a cellular service area 11. In addition, the system 10 includescells 18 and 20. It will be appreciated that a plurality of other cellswith corresponding cell sites and/or cellular service areas may also beincluded in the system 10 coupled to one or more cellular switchingcenters, such as the cellular switching center 24 and the cellularswitching center 24 b.

Within each cell, such as the cell 12, there is a wireless cell orcellular site such as cell site 13 which includes an antenna 13 a whichis designed to communicate through a wireless communication medium witha communication receiver which may be combined with a mobile GPSreceiver such as the receiver 16 shown in FIG. 1. An example of such acombined system having a GPS receiver and a communication system isshown in FIG. 3A and may include both a GPS antenna 77 and acommunication system antenna 79.

Each cell site is coupled to a cellular switching center. In FIG. 1,cell sites 13, 15, and 19 are coupled to switching center 24 throughconnections 13 b, 15 b and 19 b respectively and cell site 21 is coupledto a different switching center 24 b through connection 21 b. Theseconnections are typically wire line connections between the respectivecell site and the cellular switching centers 24 and 24 b. Each cell siteincludes an antenna for communicating with communication systemsserviced by the cell site. In one example, the cell site may be acellular telephone cell site which communicates with mobile cellulartelephones in the area serviced by the cell site. It will be appreciatedthat a communication system within one cell, such as receiver 22 shownin cell 4, may in fact communicate with cell site 19 in cell 18 due toblockage (or other reasons why cell site 21 cannot communicate with thereceiver 22).

In a typical embodiment of the present invention, the mobile GPSreceiver 16 includes a cell based communication system which isintegrated with the GPS receiver such that both the GPS receiver and thecommunication system are enclosed in the same housing. One example ofthis is a cellular telephone having an integrated GPS receiver whichshares common circuitry with the cellular telephone transceiver. Whenthis combined system is used for cellular telephone communications,transmissions occur between the receiver 16 and the cell site 13.Transmissions from the receiver 16 to the cell site 13 are thenpropagated over the connection 13 b to the cellular switching center 24and then to either another cellular telephone in a cell serviced by thecellular switching center 24 or through a connection 30 (typicallywired) to another telephone through the land-based telephonesystem/network 28. It will be appreciated that the term wired includesfiber optic and other non wireless connections such as copper cabling,etc. Transmissions from the other telephone which is communicating withthe receiver 16 are conveyed from the cellular switching center 24through the connection 13 b and the cell site 13 back to the receiver 16in the conventional manner.

The remote data processing system 26 (which may be referred to in someembodiments as a GPS server or a location server) is included in thesystem 10 and is used to determine the state (e.g. the position and/orvelocity and/or time) of a mobile GPS receiver (e.g. receiver 16) usingGPS signals received by the GPS receiver. The GPS server 26 may becoupled to the land-based telephone system/network 28 through aconnection 27, and it may also be optionally coupled to the cellularswitching center 24 through the connection 25 and also optionallycoupled to center 24 b through the connection 25 b. It will beappreciated that connections 25 and 27 are typically wired connections,although they may be wireless. Also shown as an optional component ofthe system 10 is a query terminal 29 which may consist of anothercomputer system which is coupled through the network 28 to the GPSserver 26. This query terminal 29 may send a request, for the positionand/or velocity of a particular GPS receiver in one of the cells, to theGPS server 26 which then initiates a conversation with a particular GPSreceiver through the cellular switching center in order to determine theposition and/or velocity of the GPS receiver and report requestedinformation back to the query terminal 29. In another embodiment, aposition determination for a GPS receiver may be initiated by a user ofa mobile GPS receiver; for example, the user of the mobile GPS receivermay press 911 on the cell phone to indicate an emergency situation atthe location of the mobile GPS receiver and this may initiate a locationprocess in the manner described herein.

It should be noted that a cellular based or cell based communicationsystem is a communication system which has more than one transmitter,each of which serves a different geographical area, which is predefinedat any instant in time. Typically, each transmitter is a wirelesstransmitter which serves a cell which has a geographical radius of lessthan 20 miles, although the area covered depends on the particularcellular system. There are numerous types of cellular communicationsystems, such as cellular telephones, PCS (personal communicationsystem), SMR (specialized mobile radio), one-way and two-way pagersystems, RAM, ARDIS, and wireless packet data systems. Typically, thepredefined geographical areas are referred to as cells and a pluralityof cells are grouped together into a cellular service area, such as thecellular service area 11 shown in FIG. 1, and these pluralities of cellsare coupled to one or more cellular switching centers which provideconnections to land-based telephone systems and/or networks. Servicearea are often used for billing purposes. Hence, it may be the case thatcells in more than one service area are connected to one switchingcenter. For example, in FIG. 1, cells 1 and 2 are in service area 11 andcell 3 is in service area 13, but all three are connected to switchingcenter 24. Alternatively, it is sometimes the case that cells within oneservice area are connected to different switching centers, especially indense population areas. In general, a service area is defined as acollection of cells within close geographical proximity to one another.Another class of cellular systems that fits the above description issatellite based, where the cellular basestations or cell sites aresatellites that typically orbit the earth. In these systems, the cellsectors and service areas move as a function of time. Examples of suchsystems include Iridium, Globalstar, Orbcomm, and Odyssey.

FIG. 2 shows an example of a GPS server 50 which may be used as the GPSserver 26 in FIG. 1. The GPS server 50 of FIG. 2 includes a dataprocessing unit 51 which may be a fault-tolerant digital computersystem. The SPS server 50 also includes a modem or other communicationinterface 52 and a modem or other communication interface 53 and a modemor other communication interface 54. These communication interfacesprovide connectivity for the exchange of information to and from thelocation server shown in FIG. 2 between three different networks, whichare shown as networks 60, 62, and 64. The network 60 includes thecellular switching center or centers and/or the land-based phone systemswitches or the cell sites. An example of this network is shown in FIG.1 wherein the GPS server 26 represents the server 50 of FIG. 6. Thus thenetwork 60 may be considered to include the cellular switching centers24 and 24b and the land-based telephone system/network 28 and thecellular service area 11 as well as cells 18 and 20. The network 64 maybe considered to include the query terminal 29 of FIG. 1 or the “PSAP,”which is the Public Safety Answering Point which is typically thecontrol center which answers 911 emergency telephone calls. In the caseof the query terminal 29, this terminal may be used to query the server26 in order to obtain a state (e.g. position) information from adesignated mobile SPS receiver located in the various cells of the cellbased communication system. In this instance, the location operation isinitiated by someone other than the user of the mobile GPS receiver. Inthe case of a 911 telephone call from the mobile GPS receiver whichincludes a cellular telephone, the location process is initiated by theuser of the cellular telephone. The network 62, which represents the GPSreference network 32 of FIG. 1, is a network of GPS receivers which areGPS reference receivers designed to provide differential GPS correctioninformation and also to provide GPS signal data including at least aportion of the satellite navigation message such as the satelliteephemeris data to the data processing unit. When the server 50 serves avery large geographical area, a local optional GPS receiver, such asoptional GPS receiver 56, may not be able to observe all GPS satellitesthat are in view of mobile SPS receivers throughout this area.Accordingly, the network 62 collects and provides at least a portion ofthe satellite navigation message such as satellite ephemeris data anddifferential GPS correction data over a wide area in accordance with oneembodiment of the present invention.

As shown in FIG. 6, a mass storage device 55 is coupled to the dataprocessing unit 51. Typically, the mass storage 55 will include storagefor software and data for performing the GPS position calculations afterreceiving pseudoranges from the mobile GPS receivers, such as a receiver16 of FIG. 1. These pseudoranges are normally received through the cellsite and cellular switching center and the modem or other interface 53.The mass storage device 55 also includes software, at least in oneembodiment, which is used to receive and use the satellite ephemerisdata provided by the GPS reference network 32 through the modem or otherinterface 54.

In a typical embodiment of the present invention, the optional GPSreceiver 56 is not necessary as the GPS reference network 32 of FIG. 1(shown as network 62 of FIG. 2) provides the differential GPSinformation as well as providing the raw satellite navigation messagefrom the satellites in view of the various reference receivers in theGPS reference network. It will be appreciated that the satelliteephemeris data obtained from the network through the modem or otherinterface 54 may be used in a conventional manner with the pseudorangesobtained from the mobile GPS receiver in order to compute the positioninformation for the mobile GPS receiver. The interfaces 52, 53, and 54may each be a modem or other suitable communication interface forcoupling the data processing unit to other computer systems, as in thecase of network 64, and to cellular based communication systems, as inthe case of network 60, and to transmitting devices, such as computersystems in the network 62. In one embodiment, it will be appreciatedthat the network 62 includes a dispersed collection of GPS referencereceivers dispersed over a geographical region.

FIG. 3A shows a generalized combined system which includes a GPSreceiver and a communication system transceiver. In one example, thecommunication system transceiver is a cellular telephone. The system 75includes a GPS receiver 76 having a GPS antenna 77 and a communicationtransceiver 78 having a communication antenna 79. The GPS receiver 76 iscoupled to the communication transceiver 78 through the connection 80shown in FIG. 3A. In one mode of operation, the communication systemtransceiver 78 receives approximate Doppler information through theantenna 79 and provides this approximate Doppler information over thelink 80 to the GPS receiver 76 which performs the pseudorangedetermination by receiving the GPS signals from the GPS satellitesthrough the GPS antenna 77. This pseudorange is then transmitted to alocation server, such as the GPS server shown in FIG. 1 through thecommunication system transceiver 78. Typically the communication systemtransceiver 78 sends a signal through the antenna 79 to a cell sitewhich then transfers this information back to the GPS server, such asGPS server 26 of FIG. 1. Examples of various embodiments for the system75 are known in the art. For example, U.S. Pat. No. 5, 663,734 describesan example of a combined GPS receiver and communication system whichutilizes an improved GPS receiver system. Another example of a combinedGPS and communication system has been described in co-pendingapplication Ser. No. 08/652,833, which was filed May 23, 1996. Thesystem 75 of FIG. 3A, as well as numerous alternative communicationsystems having SPS receivers, may be employed with the methods of thepresent invention to operate with the GPS reference network of thepresent invention.

FIG. 3B shows one embodiment for a GPS reference station. It will beappreciated that each reference station may be constructed in this wayand coupled to the communication network or medium. Typically, each GPSreference station, such as GPS reference station 90 of FIG. 3B, willinclude a single or dual frequency GPS reference receiver 92 which iscoupled to a GPS antenna 91 which receives GPS signals from GPSsatellites in view of the antenna 91. GPS reference receivers are wellknown in the art. The GPS reference receiver 92, according to oneembodiment of the present invention, provides at least two types ofinformation as outputs from the receiver 92. Pseudorange outputs 93 areprovided to a processor and network interface 95, and these pseudorangeoutputs are used to compute pseudorange corrections in the conventionalmanner for those satellites in view of the GPS antenna 91. The processorand network interface 95 may be a conventional digital computer systemwhich has interfaces for receiving data from a GPS reference receiver asis well known in the art. The processor 95 will typically includesoftware designed to process the pseudorange data to determine theappropriate pseudorange correction for each satellite in view of the GPSantenna 91. These pseudorange corrections (and/or the pseudorange dataoutputs) are then transmitted through the network interface to thecommunication network or medium 96 to which other GPS reference stationsare also coupled. The GPS reference receiver 92 also provides in oneembodiment a representation of at least a portion of the satellitenavigation message such as a satellite ephemeris data output 94. Thisdata is provided to the processor and network interface 95 which thentransmits this data onto the communication network 96.

In one embodiment, the entire satellite navigation message istransmitted into the network from each reference receiver at a higherthan normal rate. Certain conventional GPS receivers can output raw(digital) navigation message data once every 6 seconds (which may beconsidered a normal rate); e.g. certain NovAtel GPS receivers have thiscapability. These receivers collect in a buffer the digital data of onesubframe of the navigation message (300 bits in the case of a standardGPS signal), and then provide this data at the output of the receiver byshifting out the data in the buffer (after buffering a full subframe of300 bits) once every 6 seconds. However, in one embodiment of theinvention, at least a portion of a representation of the digitalnavigation message is transmitted into the network at a rate of onceevery 600 milliseconds. This high data rate makes it possible to performa method for measuring time as described in co-pending U.S. patentapplication Ser. No. 08/794,649, filed Feb. 3, 1997. In this embodimentof the invention, a portion of the navigation message is transmittedinto the network once every 600 milliseconds by collecting in a bufferonly a portion of a subframe (e.g. 30 bits) and shifting out thisportion once the portion is collected. Thus, the packets of data whichare transmitted from the processor 95 into the network have a smallerportion of the navigation message than what could be provided at inpackets created from a buffer of one full subframe (of 300 bits). Itwill be appreciated that once the buffer has collected the portion ofthe subframe (e.g. 30 bits), the data may be shifted out into packetswhich are transmitted at very high data rates (e.g. 512K bps) over thenetwork of the present invention. These packets (containing fewer than afull subframe) are then reassembled at a receiving digital processingsystem by extracting and concatenating data from several packets torecreate the full subframe.

In one embodiment of the invention, each GPS reference station transmitsa representation of at least a portion of the satellite navigationmessage and the pseudorange data (rather than the pseudorange correctiondata). The pseudorange correction data can be derived from pseudorangeand ephemeris information for a particular satellite. Thus, a GPSreference station may transmit into the network either pseudorangecorrection data or ephemeris (or both). However, in a preferredembodiment, pseudorange data (instead of pseudorange correction data) istransmitted from each GPS reference station into the network becausecorrections from different receivers may be derived from different setsof ephemeris data, causing discrepancies in the corrections fromdifferent receivers. With this preferred embodiment, a centralcorrection processor (such as network correction processor 110 shown inFIG. 4) uses a consistent set of the most recent ephemeris data receivedfrom any of the GPS reference receivers, thus avoiding thesediscrepancies. The set is consistent because it consists of a group ofephemeris, range measurements (e.g. pseudoranges) and/or correctionsfrom a plurality of satellites which is applicable at one particularinstant in time. A set may be merged with other sets of data as long asthe times of applicability of each set overlap.

Referring back to FIG. 3B, the satellite ephemeris data output 94provides typically at least part of the entire raw 50 baud navigationbinary data encoded in the actual GPS signals received from each GPSsatellite. The satellite ephemeris data is part of the navigationmessage which is broadcast as the 50 bit per second data stream in theGPS signals from the GPS satellites and is described in great detail inthe GPS ICD-200 document. The processor and network interface 95receives this satellite ephemeris data output 94 and transmits it inreal time or near real time to the communication network 96. As will bedescribed below, this satellite ephemeris data which is transmitted intothe communication network is later received through the network atvarious location servers according to aspects of the present invention.

In certain embodiments of the present invention, only certain segmentsof the satellite navigation message may be sent to location servers inorder to lower the bandwidth requirements for the network interfaces andfor the communication network. Also, this data may not need to beprovided continuously. For example, only the first three subframes whichcontain ephemeris information rather than all 5 subframes together maybe transmitted into the communication network 96 when they containupdated information. It will be appreciated that in one embodiment ofthe present invention, the location server may use the navigationmessage data transmitted from one or more GPS reference receivers inorder to perform a method for measuring time related to satellite datamessages, such as the method described in co-pending U.S. patentapplication Ser. No. 08/794,649, which was filed Feb. 3, 1997, by NormanF. Krasner. It will be also understood that the GPS reference receiver92 decoded the different GPS signals from the different GPS satellitesin view of the reference receiver 92 in order to provide the binary dataoutput 94 which contains the satellite ephemeris data.

Typically, the packets of data are not addressed to specific locationservers and include portions of the navigation message and include anidentifier of which data was received from which satellite; in someembodiments, the packets may also specify an identifier of thetransmitting reference station. In some embodiments, the optional GPSreceiver 56 may be the primary source of navigation message data whichis used by the local location server and the network of the presentinvention may provide information on demand.

FIG. 4 shows an example of a GPS reference receiver network. In theexample of FIG. 4, the entire system 101 includes two location servers115 and 117 which are coupled to a communication network or medium 103which corresponds to the communication network 96 of FIG. 3B. Networkcorrection processors 110 and 112 are also coupled to the communicationnetwork 103. Five GPS reference stations 104, 105, 106, 107, and 108 areshown in FIG. 4. Each of these reference stations is coupled to thecommunication network 103. Each GPS reference station, such as GPSreference station 104, corresponds to the exemplary GPS referencestation 90 shown in FIG. 3B, and the communication network 103corresponds to the communication network 96 shown in FIG. 3B. It will beappreciated that the GPS reference stations, such as reference stations104-108 are dispersed over a geographical region in order to providereceiver coverage for GPS signals which may also be received by mobileGPS receivers. Typically this coverage between adjacent referencestations overlaps such that a complete geographical area is completelycovered. The geographical region for the entire network of referencestations may span the entire world or any subset thereof such as a city,a state, a nation, or a continent. Each GPS reference station, such asGPS reference station 104, provides pseudorange correction data to thecommunication network 103 and also provides the raw navigation datamessage which is used by the location servers as described herein, suchas location server 115. As described below, the location servers may befewer in number than the reference stations and thus will be processingpseudorange data from widely separated mobile GPS receivers. Forexample, one location server may be processing pseudorange data from amobile GPS receiver in California and a reference station in California,and the same location server may be processing pseudorange data for amobile GPS receiver in New York and a reference station in New York.Thus a single location server may be receiving navigation messages fromtwo or more reference stations which may be widely dispersed. As shownin FIG. 4, the communication network may be a data network such as aframe relay or ATM network or other high speed digital communicationnetwork.

FIG. 4 also shows two network correction processors 110 and 112; theseprocessors provide merged network corrections for multiple referencestations in one embodiment and may also provide ionospheric data to thelocation servers. The operation in one embodiment of a networkcorrection processor is described further below. Typically, theseprocessors determine the proper pseudorange corrections frompseudoranges and ephemeris having the same applicable time and merge theappropriate sets of corrections and ephemeris data into one set havingthe same or overlapping applicable time. The merged set is thenretransmitted on the network for receipt by the location servers whichare coupled to the network.

FIGS. 5A and 5B show in flowchart form a method of one embodiment of thepresent invention. In this method 200, each GPS reference receiverreceives satellite ephemeris data from GPS satellites in view of theparticular reference receiver and transmits the satellite ephemeris data(navigation message) into a communication network, such as a packetizeddata network 103 shown in FIG. 4. In a typical embodiment of this step201, each GPS signal from a GPS satellite in view of the particularreference receiver is decoded to provide the binary 50 bit per seconddata stream which is present in the GPS signal, and this 50 bit persecond data stream is transmitted into the communication network in realtime or near real time. In an alternative embodiment, only portions ofthis data stream may be transmitted into the network as noted above. Instep 203, each GPS reference receiver determines pseudorange correctionsfor pseudoranges to GPS satellites in view of the reference receiver;this operation may be performed in the conventional manner using acontroller computer, such as the processor and network interface 95shown in FIG. 3B. These pseudorange corrections from each GPS referencereceiver are then transmitted into the communication network, such asthe communication network 96 or network 103 of FIG. 4. In step 205, aprocessor, such as a network correction processor 110, which is coupledto the communication network, such as communication network 103,receives satellite ephemeris data and the pseudorange corrections. Thenetwork correction processor may produce a set of merged pseudorangecorrections and perform other operations as described below. Thesemerged pseudorange corrections are then transmitted into thecommunication network, such as communication network 103, in order thatthis information may be received by the various location servers whichare also coupled to the communication network.

The method continues in step 207 in which a first location serverreceives at least a portion of the navigation message, such as satelliteephemeris data, and the merged pseudorange corrections from the network.Thus, for example, location server 115 may receive navigation messagedata which has been transmitted into the network by various GPSreference stations. This data is typically provided in a near real timemanner, and typically each location server will receive at leastsatellite ephemeris data from two reference stations and often manymore. Typically, the received satellite navigation message data isdecoded by the location server to provide satellite clock and ephemerisdata and is stored on the server, allowing the location server tocalculate satellite positions and clock states on demand. This ephemerisdata is used to calculate the position of a mobile GPS receiver afterthat receiver provides pseudoranges to satellites in view of the mobileGPS receiver. Thus, in step 209, the first location server receivespseudoranges from a first mobile GPS receiver and determines a positionof the first mobile GPS receiver from satellite ephemeris data receivedfrom the network and from pseudoranges originating from the first mobileGPS receiver. The use of the network of reference stations allows thelocation server to calculate positions of mobile GPS receivers over adispersed area which corresponds to the area of coverage of a GPSreference receiver network. Thus, rather than having a single GPSreceiver located at the location server and providing ephemeris data toa location server, the dispersed network of GPS reference stations asshown in FIG. 4 allows the location server to provide positioncalculations for widely dispersed mobile GPS receivers. As shown in FIG.4, a second location server may also be coupled to the communicationnetwork 103 in order to provide position solution calculations formobile GPS receivers. It will be appreciated that in one embodiment thelocation server 117 may be a redundant/backup server for the locationserver 115 in case the location server 115 fails. Typically, eachlocation server will be a fault-tolerant computer system. In situationswhere high data processing demands may be placed on a particularlocation server due to the dense population in a region covered by thelocation server, several location servers may be deployed in this regionin addition to redundant location servers. Step 211 and 213 illustratethe use of the second location server in a method of the presentinvention. In step 211, a second location server receives satelliteephemeris data and corrected pseudorange corrections from thecommunication network. It will be appreciated that the satelliteephemeris data received from the network may be satellite-specific forthose satellites which are in view of the reference stations in thecorresponding area served by the location server 117. This may beperformed by placing header packets or other addressing data with thesatellite ephemeris data transmitted from a reference station and thecorrected pseudorange corrections in order to address the data to aparticular location server. In step 213, the second location serverreceives pseudoranges from a second mobile GPS receiver and determinesthe state (e.g. position) of the second mobile GPS receiver from thesatellite navigation message data received from the network and from thepseudoranges originating from the second mobile GPS receiver.

FIG. 6 illustrates an example of the data flow in connection with anetwork correction processor, such as the processor 110 of FIG. 4. Eachnetwork correction processor merges corrections from multiple referencestations into a single set of corrections (and adjustments) havingsubstantially the same applicable time for use by a location server. Inone embodiment, one particular location server may, if it fails toreceive correction data from a particular network correction processor,request the same information from a backup network correction processorin a geographically diverse location. Upon arrival at a networkcorrection processor, each correction set is buffered in memory forlookup and use as necessary. Atmospheric errors are removed, and thecorrections are merged to form a best estimate of ranging error due tosatellite clock and position errors (including SA dither). These mergednetwork corrections are then transmitted, along with key ionosphericdata and the most up-to-date navigation message for appropriatesatellites in view. In one particular embodiment, this information istransmitted to all designated location servers (which has beendesignated as the addressees of the corrections from the networkcorrection processor). Because each satellite vehicle is tracked by morethan one reference receiver in one embodiment, each set of networkcorrections can be checked to ensure internal consistency. Thus, apseudorange correction from a first reference station may be comparedagainst a pseudorange correction to the same satellite from an adjacentreference station to ensure internal consistency. As shown in FIG. 6,the reference stations 301 represent the geographically dispersedreference stations such as the stations 104-108 shown in FIG. 4. Thepseudorange correction data 303 and the navigation message data whichincludes, in one embodiment, at least a portion of the 50 bit datastream contained within the GPS signals is transmitted to a networkcorrection processor. The network correction processor extracts ionoparameters 310 and creates a correction set for a single epoch 309.Atmospheric delays are removed and merged corrections are created 316.The data flow of the various operations described herein is furthershown in FIG. 6.

FIG. 7 illustrates an example of the flow of data in connection with alocation server. FIG. 7 illustrates at least three different componentsof the system which are typically remotely located relative to thelocation server. The reference receiver network 401 corresponds to thereference stations 104-108 of FIG. 4. These reference stations arecoupled to the location server through a communication network, such asthe network 103 of FIG. 4. The reference receiver network 401 providescorrections and/or pseudorange data via the data network 403 andprovides at least a portion of the navigation message 405 also via thedata network. This navigation message typically includes the so-calledsatellite ephemeris data which is in one embodiment the 50 baud datastream in the GPS signals from each GPS satellite. The corrections 406are merged, and checked for internal consistency in a correctionprocessor and passed to the location server as corrections 408 and,optionally, geographic corrections, through the communication network.The navigation message data 407 is used to extract the ephemeris datafor state (e.g. position) calculations for mobile GPS receivers. Thestate (e.g. position) calculation 410 may be aided by altitude estimates412 from a terrain elevation database 411. The location server typicallyreceives on a continuous basis both the correction data and thenavigation message data via the communication network, such as thenetwork 103. It will be appreciated therefore that the source of thesatellite ephemeris data is not from a local GPS receiver which isco-located with the location server, but rather from a network of GPSreference receivers, such as the reference stations 104-108 of FIG. 4.In this manner, the location server may serve a large geographical areawhich would not be possible with a reference GPS receiver co-locatedwith the location server.

While the location server continues to receive at least a portion of thesatellite navigation message data and correction data from the GPSreference receiver network, it may receive requests for the position ofa mobile GPS receiver, which is shown as clients 424. A typicaltransaction with a mobile GPS receiver begins with the exchange of data.Typically, Doppler data 423 is provided to a mobile GPS receiver 424(based upon approximate position data from the mobile receiver or acellular network element) and then pseudorange data 425 is provided by amobile GPS receiver to a client interface 420 on the location server.This location transaction may, as pointed out above, be initiated at themobile GPS receiver by pressing 911 in the case of a cellular telephone,or it may be initiated by a remote operator 422 which may be consideredto correspond to the query terminal 29 of FIG. 1. As shown in FIG. 7,the Doppler prediction 414 is provided from the location server throughthe client interface 420 to the mobile GPS receiver 424, and the mobileGPS receiver typically responds with pseudorange data 425 which is usedin conjunction with the ephemeris data 409 to determine the position ofthe mobile GPS receiver. The position calculation may be performed withany of various conventional position calculation algorithms found intypical GPS receivers. This position, shown as navigation solution 414,may then be provided to client interface 420 which then may transferthis information through an executive module 421, which is typically asoftware module, to a remote operator 422. In one embodiment, the remoteoperator 422 is a PSAP (Public Safety Answering Point) which is thecontrol center which answers 911 telephone calls.

The client interface 420 manages the communication link between thelocation server and the client, such as a mobile GPS receiver. In oneembodiment, one client interface object is allocated to each mobile GPSreceiver by the executive interface. The client interface may typicallybe implemented by software operating on the location server. Theexecutive module 421, which is also typically software operating on thelocation server, assigns interfaces to address remote operationrequests. It also controls the interface to external databases andperforms network management and other external interactions asnecessary. Typically, a particular location server will provide multipleremote operator interfaces. For example, standard frame relay, X.25, andTCP/IP network connectivity may be provided to meet remote operatorrequirements.

While the foregoing description has assumed a certain architecture (inwhich a mobile SPS receiver receives SPS signals from SPS satellites anddetermines pseudoranges to those satellites and then transmits thepseudoranges, with a time stamp, to a location server which determinesthe mobile receiver's position), it will be appreciated that otherarchitectures may be employed with the present invention. For example, amobile SPS receiver may determine its own position by receiving SPSsignals and determining pseudoranges and by receiving and usingsatellite ephemeris data (e.g. from a location server which sendsappropriate satellite ephemeris data based on the approximate locationof the mobile SPS receiver determined from the cell site which iscommunicating with the mobile SPS receiver). In this example, thelocation server receives the satellite ephemeris data from the receiversof the reference network and upon a request for the location of themobile receiver, transmits the appropriate satellite ephemeris data tothe mobile receiver through the cell based communication system (e.g. acellular telephone system). The satellite ephemeris data which isappropriate is typically determined from an approximate location of themobile receiver; this approximate location may be determined from thelocation of the cell site which has established a cell based wirelesscommunication link with the mobile receiver. The location server maydetermine this approximate location from an identifier provided by thecell site; various techniques for determining and using the approximatelocation are described in co-pending U.S. patent application Ser. No.08/842,559, filed Apr. 15, 1997 by Norman F. Krasner, which applicationis hereby incorporated herein by reference. The approximate locationwill determine the satellites in view, and the location server may thentransmit satellite ephemeris data for those satellites through a mobileswitching center and the cell site to the mobile receiver. The locationserver may also transmit Doppler prediction data and/or satellitealmanac and/or pseudorange corrections to the mobile SPS receiver inthis example.

Although the methods and apparatus of the present invention have beendescribed with reference to GPS satellites, it will be appreciated thatthe teachings are equally applicable to positioning systems whichutilize pseudolites or a combination of satellites and pseudolites.Pseudolites are ground based transmitters which broadcast a PN code(similar to a GPS signal) modulated on an L-band carrier signal,generally synchronized with GPS time. Each transmitter may be assigned aunique PN code so as to permit identification by a remote receiver.Pseudolites are useful in situations where GPS signals from an orbitingsatellite might be unavailable, such as tunnels, mines, buildings orother enclosed areas. The term “satellite”, as used herein, is intendedto include pseudolite or equivalents of pseudolites, and the term GPSsignals, as used herein, is intended to include GPS-like signals frompseudolites or equivalents of pseudolites.

In the preceding discussion the invention has been described withreference to application upon the United States Global PositioningSatellite (GPS) system. It should be evident, however, that thesemethods are equally applicable to similar satellite positioning systems,and in, particular, the Russian Glonass system. The Glonass systemprimarily differs from GPS system in that the emissions from differentsatellites are differentiated from one another by utilizing slightlydifferent carrier frequencies, rather than utilizing differentpseudorandom codes. In this situation substantially all the circuitryand algorithms described previously are applicable with the exceptionthat when processing a new satellite's emission a different exponentialmultiplier corresponding to the different carrier frequencies is used topreprocess the data. The term “GPS” used herein includes suchalternative satellite positioning systems, including the Russian Glonasssystem.

In the foregoing specification, the invention has been described withreference to specific exemplary embodiments thereof. It will, however,be evident that various modifications and changes may be made theretowithout departing from the broader spirit and scope of the invention asset forth in the appended claims. The specification and drawings are,accordingly, to be regarded in an illustrative rather than a restrictivesense.

What is claimed is:
 1. A method of processing satellite positioninformation in a satellite positioning system (SPS), said methodcomprising: receiving at a first digital processing system a firstsatellite ephemeris data from a first SPS receiver having a first knownposition; receiving at said first digital processing system a secondsatellite ephemeris data from a second SPS receiver having a secondknown position; receiving at said first digital processing system aplurality of pseudorange data from a mobile SPS receiver; calculating aposition information of said mobile SPS receiver using said plurality ofpseudorange data and at least one of said first satellite ephemeris dataand said second satellite ephemeris data.
 2. A method as in claim 1wherein said first digital processing system calculates said positioninformation.
 3. A method as in claim 1 wherein said first digitalprocessing system is remotely positioned relative to said first knownposition and wherein said first SPS receiver is a first referencereceiver.
 4. A method as in claim 3 wherein said first digitalprocessing system is remotely positioned relative to said second knownposition, and wherein said second SPS receiver is a second referencereceiver.
 5. A method as in claim 1 wherein said first satelliteephemeris data is received from a first set of SPS satellites in view ofsaid first SPS receiver and wherein said second satellite ephemeris datais received from a second set of SPS satellites in view of said secondSPS receiver.
 6. A method as in claim 1, said method further comprising:receiving at said first digital processing system a first pseudorangecorrection data from said first SPS receiver; receiving at said firstdigital processing system a second pseudorange correction data from saidsecond SPS receiver.
 7. A method as in claim 6 wherein at least one ofsaid first pseudorange correction data and said second pseudorangecorrection data is used to correct said plurality of pseudorange datafrom said mobile SPS receiver to provide a corrected plurality ofpseudorange data.
 8. A method as in claim 7 wherein said positioninformation is calculated from said corrected plurality of pseudorangedata and from at least one of said first satellite ephemeris data andsaid second satellite ephemeris data.
 9. A method as in claim 5 whereinsaid first satellite ephemeris data comprises navigation messages fromsaid first set of SPS satellites and said second satellite ephemerisdata comprises navigation messages from said second set of SPSsatellites.
 10. A method as in claim 1, said method further comprising:receiving at a second digital processing system a first pseudorange datafrom said first SPS receiver; receiving at said second digitalprocessing system a second pseudorange data from said second SPSreceiver; performing a correction using said first pseudorange data toprovide a merged first pseudorange correction data and performing acorrection using said second pseudorange data to provide a merged secondpseudorange correction data; transmitting at least one of said mergedfirst pseudorange correction data and said merged second pseudorangecorrection data to said first digital processing system.
 11. A method asin claim 10 wherein at least one of said merged first pseudorangecorrection data and said merged second pseudorange correction data isused to correct said plurality of pseudorange data from said mobile SPSreceiver to provide a corrected plurality of pseudorange data.
 12. Amethod as in claim 11 wherein said position information is calculatedfrom said corrected plurality of pseudorange data and from at least oneof said first satellite ephemeris data and said second satelliteephemeris data.
 13. A method as in claim 12 wherein said first satelliteephemeris data is derived from navigation messages from a first set ofSPS satellites which are in view of said first SPS receiver and saidsecond satellite ephemeris data is derived from navigation messages froma second set of SPS satellites which are in view of said second SPSreceiver.
 14. A method as in claim 13 wherein said first satelliteephemeris data is received from said first SPS receiver through saidsecond digital processing system, and said second satellite ephemerisdata is received from said second SPS receiver through said seconddigital processing system.
 15. A method as in claim 12 wherein saidfirst digital processing system comprises a first fault tolerantcomputer system and said second digital processing system comprises asecond fault tolerant computer system and wherein said first pseudorangedata comprises at least one of first pseudoranges to satellites in viewof said first SPS receiver and first corrections for pseudoranges tosatellites in view of said first SPS receiver.
 16. A method as in claim12 wherein said first digital processing system is coupled to saidmobile SPS receiver through a wireless cell based communication system.17. A method as in claim 16 wherein said wireless cell basedcommunication system comprises a mobile switching center.
 18. A methodas in claim 17 wherein said first SPS receiver, said second SPSreceiver, said first digital processing system and said second digitalprocessing system are coupled together through a packet data network.19. A method as in claim 10, said method further comprising: receivingat a third digital processing system said first pseudorange data fromsaid first SPS receiver; receiving at said third digital processingsystem said second pseudorange data from said second SPS receiver;performing at said third digital processing system a correction usingsaid first pseudorange data to provide said merged first pseudorangecorrection data and performing a correction using said secondpseudorange correction data to provide said merged second pseudorangecorrection data, wherein said first digital processing system is capableof receiving said merged first pseudorange correction data and saidmerged second pseudorange correction data from said third digitalprocessing system.
 20. A system for processing satellite positioninformation, said system comprising: a plurality of satellitepositioning system (SPS) reference receivers, each having a knownposition, said plurality of SPS reference receivers being dispersed overa geographical region, each of said plurality of SPS reference receiverstransmitting, into a communication network, satellite ephemeris datareceived from satellites in view of each of said plurality of SPSreference receivers; a plurality of digital processing systems, eachcoupled to said communication network to receive satellite ephemerisdata transmitted through said communication network, said plurality ofdigital processing systems comprising a first digital processing systemand a second digital processing system, said first digital processingsystem receiving a first plurality of pseudorange data from a firstmobile SPS receiver and calculating a first position information of saidfirst mobile SPS receiver from said first plurality of pseudorange dataand from satellite ephemeris data received from said communicationnetwork, and said second digital processing system receiving a secondplurality of pseudorange data from a second mobile SPS receiver andcalculating a second position information of said second mobile SPSreceiver from said second plurality of pseudorange data and fromsatellite ephemeris data received from said communication network.
 21. Asystem as in claim 20 wherein said first digital processing system iscommunicatively coupled to said first mobile SPS receiver through awireless cell based communication system, and said second digitalprocessing system is communicatively coupled to said second mobile SPSreceiver through said wireless cell based communication system.
 22. Asystem as in claim 21 wherein said communication network is a packetdata network.
 23. A system as in claim 21 wherein said first digitalprocessing system is remotely located relative to at least some of saidplurality of SPS reference receivers.
 24. A system as in claim 21wherein said plurality of SPS reference receivers comprises a first SPSreference receiver and a second SPS reference receiver, and wherein saidfirst SPS reference receiver transmits into said communication network afirst satellite ephemeris data which is obtained from navigationmessages received from a first set of SPS satellites which are in viewof said first SPS reference receiver, and wherein said second SPSreference receiver transmits into said communication network a secondsatellite ephemeris data which is obtained from navigation messages froma second set of SPS satellites which are in view of said second SPSreference receiver.
 25. A system as in claim 24 wherein said firstdigital processing system is capable of using said first satelliteephemeris data and said second satellite ephemeris data in calculatingsaid first position information of said first mobile SPS receiver andsaid second digital processing system is capable of using said firstsatellite ephemeris data and said second satellite ephemeris data incalculating said second position information of said second mobile SPSreceiver.
 26. A system as in claim 24 wherein said first and said seconddigital processing systems receive a first pseudorange correction dataderived from data from said first SPS reference receiver and a secondpseudorange correction data derived from data from said second SPSreference receiver.
 27. A system as in claim 26 wherein said first SPSreference receiver transmits said first pseudorange correction data intosaid communication network and said second SPS reference receivertransmits said second pseudorange correction data into saidcommunication network.
 28. A system as in claim 27 wherein at least oneof said first pseudorange correction data and said second pseudorangecorrection data is used to correct said first plurality of pseudorangedata to provide a first merged plurality of pseudorange data and whereinsaid first position information is determined from said first mergedplurality of pseudorange data and at least one of said first satelliteephemeris data and said second satellite ephemeris data.
 29. A system asin claim 24 further comprising: a further digital processing systemcoupled to said communication network, said further digital processingsystem receiving a first pseudorange data from said first SPS referencereceiver and receiving a second pseudorange data from said second SPSreference receiver, said further digital processing system performing acorrection on said first pseudorange data to provide a merged firstpseudorange correction data and performing a correction on said secondpseudorange data to provide a merged second pseudorange correction data,and said further digital processing system transmitting at least one ofsaid merged first pseudorange correction data and said merged secondpseudorange correction data to said first digital processing system. 30.A computer readable storage medium containing executable computerprogram instructions which when executed cause a first digitalprocessing system to perform a method comprising: receiving at saidfirst digital processing system a first satellite ephemeris data from afirst satellite positioning system (SPS) receiver having a first knownposition; receiving at said first digital processing system a secondsatellite ephemeris data from a second SPS receiver having a secondknown position; receiving at said first digital processing system aplurality of pseudorange data from a mobile SPS receiver; calculating aposition information of said mobile SPS receiver using said plurality ofpseudorange data and at least one of said first satellite ephemeris dataand said second satellite ephemeris data.
 31. A computer readablestorage medium as in claim 30 wherein said first digital processingsystem is remotely positioned relative to said first known position andwherein said first SPS receiver is a reference receiver.
 32. A computerreadable storage medium as in claim 30 wherein said first satelliteephemeris data is received from a first set of SPS satellites in view ofsaid first SPS receiver and wherein said second satellite ephemeris datais received from a second set of SPS satellites in view of said secondSPS receiver.
 33. A computer readable storage medium as in claim 30,said method further comprising: receiving at said first digitalprocessing system a first pseudorange correction data derived from saidfirst SPS receiver; receiving at said first digital processing system asecond pseudorange correction data derived from said second SPSreceiver.
 34. A computer readable storage medium as in claim 33 whereinat least one of said first pseudorange correction data and said secondpseudorange correction data is used to correct said plurality ofpseudorange data from said mobile SPS receiver to provide a correctedplurality of pseudorange data.
 35. A computer readable storage medium asin claim 34 wherein said position information is calculated from saidcorrected plurality of pseudorange data and from at least one of saidfirst satellite ephemeris data and said second satellite ephemeris data.36. A system for processing satellite position information, said systemcomprising: a communication medium; a first satellite positioning system(SPS) reference receiver having a first known position and having afirst communication interface which is coupled to said communicationmedium, said first SPS reference receiver transmitting a first satelliteephemeris data into said communication medium; a second SPS referencereceiver having a second known position and having a secondcommunication interface which is coupled to said communication medium,said second SPS reference receiver transmitting a second satelliteephemeris data into said communication medium; and a first digitalprocessing system coupled to said communication medium to receive atleast one of said first satellite ephemeris data and said secondsatellite ephemeris data and to provide satellite information for amobile SPS receiver in order to determine a navigation solution of aposition information for said mobile SPS receiver wherein said mobileSPS receiver is coupled to a wireless cellular receiver which receivessaid satellite information and provides said satellite information tosaid mobile SPS receiver.
 37. A system as in claim 36 wherein said firstsatellite ephemeris data is received from a first set of SPS satellitesin view of said first SPS reference receiver and wherein said secondsatellite ephemeris data is received from a second set of SPS satellitesin view of said second SPS reference receiver.
 38. A system as in claim37 wherein said communication medium comprises a packet data network,and wherein said first communication interface and said secondcommunication interface respectively provide said first satelliteephemeris data and said second satellite ephemeris data in packet dataform.
 39. A system as in claim 37 wherein said first SPS receivertransmits a first pseudorange data into said communication medium andsaid second SPS receiver transmits a second pseudorange data into saidcommunication medium and wherein said first pseudorange data comprisesat least one of first pseudoranges to satellites in view of said firstSPS reference receiver and first corrections for pseudoranges tosatellites in view of said first SPS reference receiver.
 40. A system asin claim 39, said system further comprising: a second digital processingsystem which is coupled to said communication medium, said first digitalprocessing system receiving said first pseudorange data and receivingsaid second pseudorange data, and wherein said first digital processingsystem corrects said first pseudorange data to provide a first correctedpseudorange correction data which is transmitted into said communicationmedium and corrects said second pseudorange data to provide a secondcorrected pseudorange correction data which is transmitted into saidcommunication medium.
 41. A system as in claim 36 wherein said satelliteinformation comprises at least one of satellite ephemeris data forsatellites in view of said mobile SPS receiver or Doppler predictiondata for said satellites in view or satellite almanac data and whereinsaid satellite information is transmitted to said mobile SPS receiverfrom said first digital processing system, and wherein said satelliteephemeris data for satellites in view of said mobile SPS receiver isobtained from at least one of said first satellite ephemeris data andsaid second satellite ephemeris data.
 42. A system as in claim 41wherein said mobile SPS receiver determines said navigation solution.43. A system for transmitting satellite ephemeris information, saidsystem comprising: a communication medium; a first satellite positioningsystem (SPS) reference receiver having a first known position and havinga first communication interface which is coupled to said communicationmedium, said first SPS reference receiver transmitting first packets ofa first satellite ephemeris data into said communication medium, each ofsaid first packets having less than a subframe of satellite ephemerisdata; a second SPS reference receiver having a second known position andhaving a second communication interface which is coupled to saidcommunication medium, said second SPS reference receiver transmittingsecond packets of a second satellite ephemeris data into saidcommunication medium, each of said second packets having less than asubframe of satellite ephemeris data.
 44. A system as in claim 43wherein said first satellite ephemeris data is received from a first setof SPS satellites in view of said first SPS reference receiver andwherein said second satellite ephemeris data is received from a secondset of SPS satellites in view of said second SPS reference receiver. 45.A system as in claim 44 wherein said communication medium comprises apacket data network, and wherein said first communication interface andsaid second communication interface respectively provide said firstsatellite ephemeris data and said second satellite ephemeris data inpacket data form.
 46. A system as in claim 44 wherein said communicationmedium comprises a packet data network, and wherein said firstcommunication interface provides said first satellite ephemeris data inpacket data form.
 47. A system as in claim 44 wherein said first SPSreceiver transmits a first pseudorange data into said communicationmedium and wherein said first pseudorange data comprises at least one offirst pseudoranges to satellites in view of said first SPS referencereceiver and first corrections for pseudoranges to satellites in view ofsaid first SPS reference receiver.
 48. A system as in claim 44 whereinsaid first SPS receiver transmits a first pseudorange data into saidcommunication medium and said second SPS receiver transmits a secondpseudorange data into said communication medium and wherein said firstpseudorange data comprises at least one of first pseudoranges tosatellites in view of said first SPS reference receiver and firstcorrections for pseudoranges to satellites in view of said first SPSreference receiver.
 49. A system as in claim 48, said system furthercomprising: a first digital processing system which is coupled to saidcommunication medium, said first digital processing system receivingsaid first pseudorange data and receiving said second pseudorange data,and wherein said first digital processing system corrects said firstpseudorange data to provide a first corrected pseudorange correctiondata which is transmitted into said communication medium and correctssaid second pseudorange data to provide a second corrected pseudorangecorrection data which is transmitted into said communication medium. 50.A system as in claim 48, said system further comprising: a first digitalprocessing system which is coupled to said communication medium, saidfirst digital processing system receiving said first pseudorange data,and wherein said first digital processing system corrects said firstpseudorange data to provide a first corrected pseudorange correctiondata which is transmitted into said communication medium.
 51. A systemas in claim 43 wherein said first satellite ephemeris data is receivedfrom a first set of SPS satellites in view of said first SPS referencereceiver.
 52. A system for processing satellite position information,said system comprising: a communication medium; a first satellitepositioning system (SPS) reference receiver having a first knownposition and having a first communication interface which is coupled tosaid communication medium, said first SPS reference receivertransmitting first packets of a first satellite ephemeris data into saidcommunication medium, each of said first packets having less than asubframe of satellite ephemeris data such that said first packets aretransmitted into said communication medium at a packets per second ratewhich is greater than one packet per 6 seconds.